Increasing the reactivity of cellulose to esterification reagents



Patented Sept. 12, 1939 UNITED STATES PATENT OFFICE INCREASING THE REACTIVITY OF CELLU- LOSE TO ESTERIFICATION REAGENTS Arnold Marschall, many, assignor Freiburg-in-Breisgau, Gerto E. I. du Pont de Nemours &

Company, Wilmington, Dcl., a corporation of Delaware 12 Claims.

This invention relates to cellulosic material and process of producing same; more particularly, it relates to a process for the treatment of cellulose with a salt whereby to greatly increase the reactivity of the cellulose to a subsequent acetylation or esterification reaction.

The various forms of cellulose which are available commercially have varying degrees of chemical reactivity, depending, among other factors, on whether the source of the cellulose is cotton, cotton linters, wood pulp, Wood chips, sisal, bagasse, and the like, and in accordance with the method by which the cellulose has been purified, and the extent of the purification treatment. Thus, cellulose derived from wood pulp is generally more diflicult to esterify than cellulose derived from cotton or cotton linters. It is therefore an object of the present invention to influence and control the esterifying reactivity of cellulose, particularly cellulose which has a low chemical reactivity and is therefore diflicult to esterify by previously known e'sterification processes.

Another object of the present invention is to provide a process for the treatment ofcellulose whereby to insure a more rapid and more uniform penetration of the cellulose by the esterification reagents.

A still further object of the present invention from the group consisting of sodium, potassium,

lithium, ammonium, amine, and substituted amine salts of an acid taken from the group consisting of sulfuric, hydrochloric, perchloric, phosphorlc, and similar strong inorganic acids. The treatment of the cellulosie material by the abovedescribed salts is carried out prior to the-treatment of the cellulose with any of the usual esterifying agents, or agents especially preparing the cellulose for esterification, such as acetic anhydride, acetic acid, sulfuric acid or the like. The salts of the present invention with which the cellulosic material is to be treated have little,"if any, swelling action on the cellulose.

In accordance with the process of the present invention the treatment of the cellulosic material is preferably carried out while the cellulose is still in a completely open and swollen condition from its manufacture. By so proceeding, the cellulose veniently be made a standard practice, and

I fibers will be uniformly impregnated with the salt substantially throughout their structure. To this end the application of the salt may conpart, or a continuation, of the final washing step in the customary methods of manufacturing cellulose. The cellulose is preferably treated with an aqueous solution of the salt in such concentration thatthe salt will be present-in a quantity of 0.1 to 3% based on the dry weight of the cellulose. The cellulosic material impregnated with the salt, before esterification, is preferably dried to a moisture content of less than 12%, based on .the weight of the dry cellulose. The drying may be carried out by any suitable, known drying method which will not remove the salt.

be understood that the invention is not to be limited by the examples.

Example 1 Seventy-five kilograms of sulfite wood pulp cellulose is continuously agitated with a solution of- 10 kilograms of ammonium perchlorate dissolved in 600 liters of water for a suitable period of time, after which the liquid is pressed or centrifuged off and thewood pulp dried. The dried wood pulp has 1.3 to 2.0% of ammonium perchlorate uniformly distributed and deeply embedded throughout the cellulose fibers. After acetylation by a, conventional. acetylation procedure, for example, the procedure described in U. S. No. 1,543,310, the ammonium perchlorate impregnated pulp surprisingly yields a cellulose acetate exhibiting the following improvement over the cellulose acetate derived by the same acetylation procedure from the same pulp without the tion at 15 C. in c. g. s. units) Example 2 Wood pulp cellulose, prepared according to while still somewhat wet, and swollen from the customary washing, is

salt pretreatment:

' Pre- Untreated treated pulp pu Time of acetylation in minutes 8'7 Clarity: comparative transparency of a layer of the acetylated solution in cm 205 139 Filterability in cc. per unit of time "288 87 Viscosity-(of a. 7% acetone solumixed with a solution of 15 kilograms of am- Since it is obvious that many changes and monium sulfate dissolved in 600 liters of water modifications of the above described processes can for a suitableperiod of time, after which the be made without departing from the nature and liquid is pressed or centrifuged off. After air dryspirit of the invention, it is to be understood that 5 ing, the wood pulp exhibits a salt content of the invention is not to be limited except as set 5 1.5-2.1% ammonium sulfate uniformly distributed forth in the appended claims.

throughout the fibers, including the interiors I claim:

thereof. Upon acetylation by any standard pro- 1. The process of increasing the reactivity of I cedure, the ammonium sulfate impregnated wood cellulose to esterification reagents which comm pulp acetylates quite rapidly to a cellulose aceprises the step of treating the cellulose, prior to tate superior in clarity and filterability to the its treatment with any esterification reagent, cellulose acetate derived by the same acetylation with a solution of a salt takenfrom the group procedure from the same pulp without the salt consisting of sodium, potassium, lithium, am-

' pretreatment.- monium, amine, and substituted aminesalts of Among the salts which may be used, in acan acid taken from the group consisting of sulcordance with the present invention, for the prefuric, hydrochloric, 'perchloric and phosphoric treatment of cellulosic material, the pentavalent acids, and drying the cellulose,'impregnated with nitrogen-containing salts of hydrochloric, sulthe salt, to a moisture content of less than 12%, furic, phosphoric and perchlorlc acids have been based on the weight of the dry cellulose. I

found tobe particularly useful. Particularly good 2. The process of increasing the reactivity of 20 results have been obtained with ammonium chlocellulose to esterification reagentswhichcomprises ride, ammonium phosphate, trimethylamt'ne hythe step of treating the cellulose, prior to its drochloride, triethylamine hydrochloride, tritreatment with any esterification reagen with ethylamine perchlorate, triethanolamine per-. an aqueous solution of a salt taken from the chlorate, triethanolamine hydrochloride, tetragroup consisting of sodium, potassium, lithium, 2

methyl ammonium chloride, tetraethyl ammoniammonium, amine, and substituted amine salts um chloride, and tetraethyl ammonium perof an acid taken from the group consisting of chlorate. Certain alkaline salts of the above sulfuric, hydrochloric, perchloric and phosphoric mentioned acids have also given very useful reacids, and drying the cellulose, impregnated with suits, for example sodium, chloride, potassium the salt, to a moisture content of less than 12%, 30 chloride, sodium sulfate, potassium perchlorate, based on the weight of the dry cellulose.

etc. The present invention does not comprehend 3. The process of increasing the reactivity of the use of salts having substantial swelling ac-- cellulose to esterification reagents which com--v tion on cellulose under normal conditions. prises the step of treating the cellulose, prior to The esterification of the salt impregnated celluits treatment with any esterification reagent, with 5 lose may be conducted in accordance with praca solution of a water-soluble, pentavalent nitrotically any of the known esterification methods, gen-containing salt, and drying the cellulose, im- Thus, the esterification maybe performed in pregnated with the salt, to a moisture content such a manner that the resulting cellulose ester of less than 12%, based on the weight of the dry dissolves or disperses to form a dope or, if desired, cellulose. 40 in such a fashion in the presence of a cellulose 4. The process of increasing the reactivity of ester nonsolvent that the resulting cellulose ester cellulose to esterification reagents which cornretains the fibrous form of the original cellulose. prises the step of treating the cellulose, prior to If desired, instead of cellulose acetate, the esteriits treatment with any esterification reagent,

fication of such pretreated cellulose may be d" W th an q e 5011mm! O a water-soluble, 45 rected to the preparation of other simple and pentavalent nitrogen-containing salt, and dryingmixed organic esters of cellulose, such as celluthe cellulose, impregnated with the salt, to a lose formate, cellulose propionate, cellulose bumoisture content of less than 12%, based on the tyrate, cellulose acetopropionate, cellulose acetoweight of the dry cellulose.

,0 butyrate, cellulose acetate succinate, cellulose 5. The process of increasing the reactivity of acetate phthalate, and cellulose acetate stearate; cellulose to esterification reagents which com- The process of the invention increases the prises the step of treating the cellulose, prior to chemical reactivity of. the cellulose and makes its treatment with any esterification reagent, with available for esterification certain commercially a solution of a water-soluble, pentavalent nitrooccurring low grade celluloses previously generalgen-containing salt in such concentration as to ly considered unsuitable because of their known impart to the cellulosic material 0.1 to 3% salt resistance toward estification. The pretreatment based on the weight of the cellulose, and drying appearsalso to permit the esterifying reagents, 'the cellulose, impregnated with the salt, to a such as acetic acid, acetic anhydride, and sulfuric moisture content of less than 12%, based on the (.0 acid, to penetrate more uniformly and rapidly weight of the dry cellulose.

into the interiors of the cellulose fibers, and re- 6'. The process of increasing the reactivity of sultsinamore rapid esterification. The cellulose, cellulose to esterification reagents which compretreated by the process of the invention, seemprises the step of'tfeating the cellulose, prior to ingly yields upon esterification a cellulose ester of its treatment with any esterification reagent, and

more uniform quality than normally, judging by while the cellulose is in an open or swollen condithe superior clarity and filterability exhibited. o w t a Solution of a Water-Soluble, D t Such uniformity arises, it is believed, from the valent nitrogen-containing salt, and drying the salts being uniformly and deeply distributed in cellulose, impregnated with thesalt, to a mo sture the fiber interior by the salt solutior treatment content of less than 12%, based on the weight of and from the salts being embedded in the fibers the dry cellulose. 70 by drying before subjecting the fibers to esterify- 7. The process of increasing the reactivity of ing reagents. The cellulose esters may, of course, cellulose to esterification reagents which combe converted by usual methods into useful strucprises the step of treating the cellulose, prior to tures, such as threads, films, lacquers, and its treatment with any esterification reagent, with plastics, a solution of triethanolamine perchlorate. n

' taken from 15 'tassium, nun

tuted amine salts of an acid taken from the group 8. Cellulose, having a moisture content of less than 12% based on the weight of the dry cellulose, and having an increased reactivity to esterificasulfuric, hy ochloric, perchloric and phosphoric, acids. 1

'9. Cellulose, having a moisture content of less than 12%, based on the weight of the dry cellulose, and having an increased reactivity to esterification reagents, containing 0.1 to 3% of a salt the group consisting of sodium, po-

um, ammonium, amine, and substiconsisting of sulfuric, hydrochloric, perchloric and phosphoric acids.

10. Cellulose, having a moisture content of less than 12%, based on the weight of the dry cellulose, and having an increased reactivity to esterification reagents, containing a water-soluble, pentavalent nitrogen-containing salt.

11. Cellulose, having a moisture content of less than 12%, based on the weight of the dry cellulose, and having an increased reactivity to esterification reagents, containing 0.1 to 3% of a water- 

